Past and Future Use of Default Assumptions and Uncertainty Factors: Default Assumptions, Misunderstandings, and New Concepts

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Notes

¹Many groups used different terms in risk assessment. The definition of several terms used when discussing default assumptions in this article are provided as: (1) adverse effects are either biochemical change, functional impairment, or pathologic lesion, which impairs performance and reduces the ability of an organism to respond to additional challenge, (2) adaptive effect enhances an organism's performance as a whole and/or its ability to withstand a challenge; an increase in hepatic smooth endoplasmic reticulum is an example of an adaptive effect, if hepatic metabolism reduces the chemical's toxicity, (3) compensatory effect maintains overall function without enhancement or significant cost. Increased respiration due to metabolic acidosis is an example of a compensatory effect, (4) critical effect is the first adverse effect or its known and immediate precursor that occur as dose rate increases, (5) severity is the degree to which an effect changes and impairs the functional capacity of an organ system (USEPA 2005).